Field of the Invention
Embodiments of the present invention relate in general to evaluating subterranean geophysical formations in the industry of mineral exploration and recovery, and in particular to machines, systems, and methods for sonic logging to evaluate geophysical formations.
Description of the Related Art
Sonic logging can be used to characterize a geophysical formation. The process of sonic logging can involve lowering a transducer into a wellbore, generating a sound, or wavelength, so that the wavelength is refracted by the geophysical formation, and recording the refracted wavelengths by an array of receivers. The time that it takes the wavelengths to travel through the formation, which can be called the “travel time,” can be used to derive the velocity of the formation. The velocity of the formation can be used to determine various characteristics of the formation.
Sonic logging can involve various types of sound energy, or wavelengths. One of the more useful types of wavelengths is the pressure wave (“p-wave”), which is a compressional or longitudinal wave. Other wavelength types include the shear wave (“s-wave”), the Rayleigh waves, Stoneley waves, and mud waves. The p-waves are generally the “first arrival” waves because they are the fastest of the wavelength types used for sonic logging and, thus, arrive at the receivers before the other types of wavelengths. The time that it takes the p-waves to travel from a sound source to one or more receivers can be used to characterize the formation because the velocity of the p-wave depends on the properties of the geophysical formation. Density, porosity, fluid presence, and fluid type each predictably affect the velocity of the p-wave through the formation.